Water-miscible, storage-stable auramine base solution and process of preparing same



United States Patent 3,373 199 WATER-MISCIBLE, STORAGE-STABLE AURAMINEBASE SQLUTION AND PROCESS OF PREPARING SAME Werner Victor Cohen, GlenFarms, Md, and Eugene Coley Dietemann, Woodstown, N.J., assignors to E.I.

du Pont de Nemours and Company, Wilmington, Del., a corporation ofDelaware No Drawing. Filed May 28, 1962, Ser. No. 197,921 4 Claims. (Cl.260-566) This invention is directed to a novel composition of matterwhich furnishes readily an aqueous dye bath for use in the production ofauramine-colored paper sheets or paper pulp.

The bright yellow dye known as auramine (C1. Basic Yellow 2, C.l.41,000) is the hydrochloride of 4,4-bis-(dimethylamino)benzophenonimine. Its synthesis is described briefly inThe Chemistry of Synthetic Dyes and Pigments (edited by H. A. Lnbs), onpage 246. It is generally sold in powder form for use primarily in thedyeing of paper from an aqueous solution of the color.

Auramine dissolves in cold water to the extent of about 0.5%. It haspoor water solution stability, hydrolyzing quite rapidly in diluteaqueous solutions at slightly elevated temperatures according to theequation (onom (3:0 -I- NH-lCl Auramine Therefore, it is the practice tomake up fresh dye solutions from the dye powder for each dyeingoperation or short series of dyeings.

The hydrolysis of auramine in a dilute aqueous solution is readilyobserved by the turbidity which accompanies the formation of Michlersketone, which is not a dye. Since the dyeing strength is proportional tothe concentration of auramine base, any form or preparation of this dyewhich initially .forms turbid solutions when dis-solved in water is notdesirable in the trade.

In addition, auramine in powder form is dusty to handle and dissolvesslowly, particularly in water which approaches ice temperature as inwinter-time dyeing operations.

Accordingly, it is a primary object of this invention to provide a noveland marketable form for the aforementioned dye which avoids the dustingtroubles, is readily soluble in water, does not readily hydrolyze underthe conditions of use, and has reasonably good storage stability topermit its packaging and handling in commerce.

It is a further object to provide a process for preparing the heretoforedescribed novel dye composition.

These and other objects will become apparent in the followingdescription and claims.

Now we have found that all the aforegoing objects can be achieved bydissolving auramine base in essentially glacial acetic acid (or inacetic acid diluted by anhydrous hydroxyacetic acid), whereby to form acommercial solution containing up to 50% by weight of the color,calculated as base, and preferably, 35 to 40%, provided care is taken toexclude from the solution any substantial quantities of mineral acidity(e.g. HCl), water-soluble salts, auramine dye itself (i.e. thehydrochloride of the base) and Michlers ketone. By auramine base, ofcourse,

3,373,l9 Patented Mar. 12, 1%58 is meant 4,4-bis(dimethylamino)benzophenoneimine, i.e., the compound of formula By water-soluble saltshereinabove, we mean alkali metal and ammonium salts of inorganic andorganic acids (e.g. NaCl or ammonium acetate). By substantial quantitleswe mean quantities sufiicient to produce a visible precipitate orturbidity in the acetic acid solution. Thus, mineral acid salts areessentially insoluble in glacial acetic acid and therefore will producetheir own precipitate in the system; on the other hand, sodium acetateis soluble in glacial acetic acid to about 5%. Concentrations thereof,however, of about 5% have a salting out effect on the dye, auramine baseacetate, whereas concentrations of 2% of sodium acetate have no illeliect on the stability of the system as judged by dye tests afterstorage for two months. Accordingly, exclusion of substantial quantitiesin this invention, in the case of salts soluble in acetic acid, mean-sexclusion of quantities greater than about 3% by weight.

The upper limit in amount of anhydrous hydroxyacetic acid that may bemixed with glacial acetic acid is not critical, being determined by thephysical characteristics desired for the dye solution. Sincehydroxyacetic acid is a solid, and an object of this invention is toprovide a dye solution which remains liquid at relatively lowtemperatures, a preferred upper limit for the hydroxyacetic acid isabout 30% by weight of total solvent.

Water should also be excluded from the marketable concentrated solution,but its presence is not so critical as that of the other undesirablecontaminants above mentioned, and quantities thereof up to 1.5% byweight based on the weight of the solution are not harmful to theobjects of this invention.

We find that when constituted as above, the herein described novelcomposition is stable, as defined below, and does not hydrolyzeappreciably when stored in a tightly closed container for two months at35 C. Furthermore, it dissolves readily in water to produce therein thecolor, auramine base acetate, in concentrations varying from less than0.04% (as dye base) to that of the original solution (say as high as50%), and the diluted dye solutions are themselves stable for asufiicient length of time (say 8 or even up to 24 hours at roomtemperature) to permit their practical use in coloring paper pulp in thepaper-making machine.

By contrast, aqueous solutions of only 0.5% concentration or less can bemade from ordinary standard auramine powder (HCl salt), because of poorsolubility, and these solutions become turbid after 2 to 3 hours. Thusthe usefulness of such solutions is greatly impaired after relativelyshort periods of storage, a factor which renders them unsatisfactory foruse in the trade.

For the purpose of this invention, two methods are available for testingthe degree of hydrolysis sufiered by a given composition in a givenlength of time. These are: (a) turbidity in dilute aqueous solutions and(b) dye test for dye strength.

The turbidity test is a qualitative but very sensitive test and isuseful to detect trace amounts of hydrolysis. The dye test is useful toascertain quantitatively the amount of dye which is lost by hydrolysis.In this test, the standard reference for strength is the dyeing on paperobtained from a freshly prepared dye bath containing a calculable amountof auramine base applied as auramine standard dye powder. For instance,a 10% weakness of a dyeing made from a sample of auramine baseconcentrated solution (of known initial dye content) compared r to thesame amount of dye calculated as dye base in the standard powder, showsa 10% loss of dye by hydrolysis in the concentrated solution.

The upper limit of hydrolysis permitted under the definition of storagestable in this invention is 10% by weight of auramine base after storagein a tightly closed container for two months at 35 C.

The turbidity test is made by adding a sample of the concentratedsolution of aura-mine base acetate to Water to provide a 0.04% solutioncalculated as the dye base. A clear dilute aqueous solution shows thatthe dye has not hydrolyzed to the ketone.

Without limiting this invention, the following representative examplesare given to illustrate our preferred mode of operation. Parts mentionedare by weight.

EXAMPLE 1 Part A.-Preparatin of auramine base Crude auramine (dyehydrochloride, prepared according to the Peer process, method (1) onpage 246 of Lubs, above cited), is extracted with cold water to removemost of the sodium chloride. One part of the dye thus obtained isdissolved in 20 parts of water at 60 to 65 C. The solution is clarifiedby filtration and cooled rapidly to 15 to 20 C. A 10% aqueous solutionof sodium hydroxide is added to produce and maintain a positive test foralkali on phenolphthalein test paper, and agitation is continued at 15to 20 C. until precipitation of auramine base is complete. This state isshown by a colorless or very light-colored ring when a test sample ofthe reaction mass is spotted on filter paper. The dye base is thenfiltered off, washed with cold water until free of alkali, and dried ata temperature not exceeding 60 C. until a test sample analyzes not morethan 0.5% water.

All analyses for Water content in this specification are meant to referto water contents as determined by the Karl Fischer method (Anal. Chem,vol. 23, page 1069; 1951).

If desired, ammonium hydroxide, sodium carbonate, potassium carbonate orpotassium hydroxide can be substituted for sodium hydroxide in thepresent example, the rest of the procedure being the same.

Part B.--Preparati0n of the marketable composition Thirty-five parts ofaurarnine base, prepared as in Part A, are stirred into 65 parts ofglacial acetic acid having a water content of not more than 0.08%, Whilemaintaining the solution temperature at 20 to 35 C. The solution thusobtained is clarified by filtration to remove insoluble material.Exposure to air is kept at a minimum so that the freshly preparedsolution contains not more than 0.25% water.

The clear filtrate obtained is colored and constitutes a solution ofauramine base acetate in acetic acid.

When the process of this example is repeated, exceptthat 25 parts ofauramine base and 75 parts of glacial acetic acid are employed, astorage stable concentrated dye solution is likewise obtained whichgives satisfactory results in the turbidity and dyeing tests.

Similar results are obtained when 50 parts each of anramine base andglacial acetic acid are employed in Part B of this example.

For test purposes, the filtrate may be divided and stored in a series ofclosed containers for several months at temperatures ranging from to 35C. We have observed that all such stored samples remain fluid during thestorage period, and that the samples stored even as high as 35 C. arestable against hydrolysis for at least two months. Thus, (1) dilution ofthe concentrated solution in water to form a 0.04% solution as dye base(i.e. 1.2 grams of the concentrated solution per liter of water), showsessentially no turbidity, and (2) a sample of the concentrated dyesolution when subjected to comparative dyeing test against a sample ofauramine standard dye powder (as indicated hereinabove) shows fulldyeing strength.

If the procedure of Part B above is repeated except using acetic acidwhich contains 0.6% moisture (which rises to about 0.7% after the dyeconcentrate has been stored for two months at 20 to 35 C.), the dyesolution 5 still gives excellent results both by the turbidity test andby the comparative dyeing strength test above referred to.

When Part B is repeated except using 65 parts of propionic acid in lieuof the same quantity of acetic acid, the resultant concentrate analyzes1.2% Water after two months storage and when diluted as above to a dyeconcentration of 0.04% it exhibits appreciable turbidity.

Similar experiments have shown that when acetic acid is employed assolvent, the water content of the system generally rises with storage,but that as long as the final water content does not exceed 1.5 itshydrolytic stability is not visibly affected. In other words, upondilution with water to a dye concentration of about 0.04%, no more thanslight turbidity is observed.

EXAMPLE 2 Mixture of acetic and hydroxyacetic acids Thirty-seven partsof auramine base, prepared as in Part A of Example 1, are stirred into amixture of 57 parts of glacial acetic and six parts of hydroxyaceticacid while maintaining the solution temperature at 20 to 35 C. The dyesolution is clarified by filtration.

In an actual experiment as in this example, analysis of the dyeconcentrate showed it to contain 0.74% moisture. Upon dilution withwater, no turbidity was observed and the dye strength test showed thesolution to be equal to the dye powder standard. When allowed to stand,however, for six Weeks at 20,to 34 C., the moisture content of thesolution rose to 1.8%, yet the solution, which showed considerableturbidity in the turbidity test, sufiered only a 5% loss in tinctorialstrength when tested by the dye strength method. In a similarexperiment, when the moisture content of the concentrated dye solutionwas kept below 1.5% (same basis) during storage for six weeks, theproductshowed no loss in tinctorial strength when dyed on paper.

Similar results were obtained in experiments Where- EXAMPLE 3 Auraminebase, free of Michlers ketone and mineral acidity, and essentially freeof water and water-soluble salts, is dissolved in glacial acetic acid at25 C. in concentrations shown in the following table. The dye solutionsare clarified by filtration and small amounts of water are added toportions of the samples A, C and E to provide the samples designated,respectively, as B, D and F. The samples are analyzed for water contentand then are stored in tightly closed containers -for two months at 20to 30 C. The above described turbidity test is made at the completion ofthe storage period.

All of the stored samples A to F show excellent dyeing strength onpaper.

EXAMPLE 4 7O Dyeing procedure One part of the auramine base solutionprepared in Part B of Example 1 is added to an aqueous slurry of parts(dry basis) of bleached sulfite pulp in 5000 5 parts of water at roomtemperature. (This may vary in normal plant practices from 2 C. in theWinter in northern localities to 38 C. in the summer in warmerclimates.) Two parts each of rosin size and aluminum sulfateoctadecahydrate [Al (SO -18H O] are then added, the mixture isthoroughly agitated for to minutes and water is added to give a total of20,000 parts. Paper sheet is then made up in the usual manner to provideyellow colored paper.

The amount of dye employed in this procedure may be varied from 0.05 to1.0 part to give lightly tinted to deeply colored dyeings. The percentby weight of air dried paper pulp in the initial slurry may vary from0.4 to 3. Likewise, the amount of rosin size and aluminum sulfate usedmay vary from about 0.5 to 3 parts and from 1 to 4 parts, respectively,or these additives may be omitted.

It will be understood that the details of the above examples may bevaried within the skill of those engaged in this art. For instance, theconcentration of the dye in the marketable solution is not critical, thelower limit being determined by economy and convenience in handling,while the upper limit (50%) is chosen to avoid unduly high viscosity inthe solution. For optimum conditions, concentrations of 35 to 40% of dyebase are recommended.

As already indicated, it is desirable to start with glacial acetic acid.Traces of moisture nevertheless enter the initial dye solution from thesolvent, from the dye base and from the atmosphere. For improvedstability, therefore, the acetic acid-dye solutions should be stored intightly closed containers, and unused portions should be handled underconditions of minimum exposure to moisture.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A water-miscible, storage-stable, coloring composi tion of matterconsisting essentially of a solution of auramine base in a solventconsisting of mixtures of acetic acid with hydroxyacetic acid containingthe latter in a quantity not exceeding 30%'by weight, said solutionbeing essentially free of mineral acids, inorganic salts, salts ofauramine base, and Michlers ketone, said solution being free of moisturein excess of 1.5 by weight and also free of acetic salts in excess ofabout 3% by weight.

2. A coloring composition as in claim 1, the quantity of auramine basetherein constituting from 25 to by Weight of the entire composition.

3. A process for preparing a water-miscible, storagestable, solution ofauramine base, which comprises (1) reacting aurmine with a water-solublealkali whereby to produce auramine base,

(2) filtering off the latter and drying the same at a temperature notexceeding C. whereby to minimize hydrolysis of the base during saiddrying step, and

(3) dissolving the dried base at a temperature not exceeding 60 C. in asolvent consisting of mixtures of acetic acid with hydroxyacetic acidcontaining the latter in a quantity not exceeding 30% by weight,dissolving step excluding contamination of the solution with moisture ina quantity exceeding 1.5% by weight.

4. A process as in claim 3 wherein the auramine base filtered off instep (2) is washed with water at a temper-a ture not exceeding 60 -C. toremove excess alkali and byproduct salts, prior to drying.

References Cited UNITED STATES PATENTS 7/1927 Lutten 892 OTHERREFERENCES CHARLES B. PARKER, Primary Examiner.

N. G. TORCHIN, A. H. WINKELSTEIN, FLOYD D.

HIGEL, Examiners.

D. LEVY, R. V. HINES, Assistant Examiners.

1. A WATER-MISCIBLE, STORAGE-STABLE, COLORING COMPOSITION OF MATTERCONSISTING ESSENTIALLY OF A SOLUTION OF AURAMINE BASE IN A SOLVENTCONSISTING OF MIXTURES OF ACETIC ACID WITH HYDROXYACETIC ACID CONTAININGTHE LATTER IN A QUANTITY NOT EXCEEDING 30% BY WEIGHT, SAID SOLUTIONBEING ESSENTIALLY FREE OF MINERAL ACIDS, INORGANIC SALTS, SALTS OFAURAMINE BASE, AND MICHLER''S KETONE, SAID SOLUTION BEING FREE OFMOISTURE IN EXCESS OF 1.5% BY WEIGHT AND ALSO FREE OF ACETIC SALTS INEXCESS OF ABOUT 3% BY WEIGHT.
 3. A PROCESS FOR PREPARING AWATER-MISCIBLE, STORAGESTABLE, SOLUTION OF AURAMINE BASE, WHICHCOMPRISES (1) REACTING AURAMINE WITH A WATER-SOLUBLE ALKALI WHEREBY TOPRODUCE AURAMINE BASE, (2) FILTERING OFF THE LATTER AND DRYING THE SAMEAT A TEMPERATURE NOT EXCEEDING 60*C. WHEREBY TO MINIMIZE HYDROLYSIS OFTHE BASE DURING SAID DRYING STEP, AND (3) DISSOLVING THE DRIED BASE AT ATEMPERATURE NOT EXCEEDING 60*C. IN A SOLVENT CONSISTING OF MIXTURES OFACETIC ACID WITH HYDROXYACETIC ACID CONTAINING THE LATTER IN A QUANTITYNOT EXCEEDING 30% BY WEIGHT, DISSOLVING STEP EXCLUDING CONTAMINATION OFTHE SOLUTION WITH MOISTURE IN A QUANTITY EXCEEDING 1.5% BY WEIGHT.